Methods of making a lignocellulose product and products resulting therefrom



United States Patent P NIETHODS OF MAKING A LIGNOCELLULOSE PRODUCT ANDPRODUCTS RESULTING THEREFROM William T. Glab, Duhuqne, Iowa, assignor,by mesne assignments, to Durel Incorporated, Dubuque, Iowa, acorporation of Iowa No Drawing. Filed Sept. so, 1958, Ser. No. 764,232

l SClaims. (Cl.106--163) This invention relates to methods of making alignocellulose product and to the products resulting therefrom.

This application is a continuation-in-part of my copending application,Serial No. 443,711, filed July 15, 1954, now US. Patent No. 2,864,715.

It is an object of this invention to provide an improved method ofmaking a rnoldable composition comprising reacting an essentially drymixture including comminuted lignocellulose and a reactant includingformaldehyde while confining the mixture of lignocellulose and reactantunder superatmospheric pressure.

Another object of this invention is to provide such a method wherein thereaction is conducted in an atmosphere of steam at about 300-500 F. forabout 4-60 minutes.

-A further object of the invention is to provide lignocellulose productsprepared by the above methods.

Other objects and advantages of the invention will be apparent from thefollowing description of several embodiments of the invention.

An important advantage of the invention appears to be the controlling ofthe reaction so that the alpha cellulose is reduced in molecular sizesufliciently to prevent swelling of subsequently fabricated products butnot to the extent that toughness of fibre is lost. This latter occursunder drastic degradation and starts to become quite serious whenapproximately 25% of the lignocellulose has been lost as either gaseousor soluble byproducts.

Another advantage appears to be the plasticization of the lignincomponent during the controlled cellulose degradation so that the lignincan subsequently be made to flow and function as a binder between thecomminuted lignocellulose particles.

Another advantage is the provision of a relatively dry system so thathigh capacity for the processing of, for example, wood waste isattained. This is not possible in a wet process such as ordinarily foundin a pulping process in which the reactor i charged with approximately90% water which takes up space as well as requires the addition of largeamounts of energy to bring the reaction medium to the propertemperature.

Another advantage is the contacting of lignocellulose or dry mixes oflignocellulose and other ingredients under superatmospheric pressurewith a vapor or combination of vapors functioning both as a heattransfer medium and as a reactant.

In the method of this invention an essentially dry mixture includingcomminuted lignocellulose and a reactant including formaldehyde isreacted as by heating while confining the lignocellulose and thereactant under supenatmospheric pressure as in an autoclave. During thereaction the lignocellulose bond is apparently broken and the lignin isreleased to operate as a binder.

It appears that the hemicelluloses are the primary constituents of thelignocellulose which are attacked by hydrolysis, but that under the highpressure and temperature of this invention a portion of the hydrolysates2,984,578 Patented May 16, 1961 are further converted to highermolecular weight materials which can function as plasticizers for theautoclave product when it is molded. At the same time a controlleddegradation of the alpha cellulose is carried out to the extent that thedesired degree of moisture stability is obtained in the molded orextruded products without an unnecessary loss of toughness. Theseactions are believed to occur although they have not been absolutelyproven.

The methods of this invention may be carried out batchwise in anautoclave or a sealed press or continuously in a continuous contactor.

The lignocellulose which appears dry to the touch actually contains upto about 30% water before the reaction begins.

The lignocellulose which may be used in this invention includes wood aswell as other lignocellulosic vegetable materials. The lignocellulose isfinely divided so that the particles are preferably not more than 2.0mesh in size as measured by a standard screen although smaller sizes arepreferred.

During the reaction which takes place in a confined atmosphere undersuperatmospheric pressure various reaction products are producedalthough the exact nature of the reactions is not understood. It appearsthat the reaction products are either inert so that the product iself isinert, have a binding action such as is true of the lignin produced, aregaseous by-products, or are polymerized. By hydrolyzing and partiallyremoving, or polymerizing the hemicelluloses to lignin type materials,the ratio of lignin and other binders to the alpha-cellulose isincreased so that the general nature of the lignocellulose mixture isdrastically changed.

The high pressure method of this invention has a number of advantagesthat are not possible with reactions taking place at ordinary pressuresand in an unconfined state. In the preferred process, steam isintroduced into the autoclave both for heating purposes and to supplymoisture for the reaction. In the high pressure method of this inventionheat transfer is much more rapid so that in general a shorter reactiontime is required. Furthermore, energy losses during the reaction aregreatiy reduced. In the ordinary reacting mixture these energy lossesresult from the release of volatile materials such as water vapor,gaseous reaction by-products and the like. As the reaction here takesplace in a confined atmosphere, no such losses occur to any materialdegree. Furthermore, the energy supplied by the steam or vapor isutilized to heat only the lignocellulose with its approximately normalmoisture contentin contrast to pulping type reactions where largequantities of water are present, requiring far greater expenditures ofenergy.

Another important advantage of this process is the close control that isobtained over the reaction. Thus the temperature of the reacting mass,and hence the rate of reaction, can be easily raised or lowered bycontrolling the rate of flow, pressure and the temperature of the heattransfer medium which may be steam, oil vapor, or other high temperaturefluids. Reactions may easily be stopped by flashing the heat transfermedium from the autoclave since the large energy loss on expansion coolsthe reacting mass below the incipient reaction point. During thepractice of the process the reacting mixture may be confined in ajacketed vessel with the heating medium introduced to the chambers inthe quantity and temperature desired.

A very important advantage of the invention is that volatile reactantsmay be used as the reacting mass is in a confined space. Volatilereactants are impossible, of course, when the reacting mass is in theopen. As a result of the rapid heat transfer achieved. by this inventionand the penetration of volatile reactants the reaction not only proceedsto completion in a much shorter time but the final product tends to bemore uniform than where the reactants are heated such as in an ordinaryprocess that depends upon surface temperautre differentials.

Tests have shown that the confining of the reacting mass in theautoclave not only causes retention of the by-products of reactionwithin the mass even when the byproducts are gaseous but also causespolymerization of all or a portion of these by-products, even some thatare gaseous. In so-called wet processes large quantities of theby-products of reaction go into solution and are lost.

Another advantage of the invention is that the vo-latile by-products areeasily collected and removed at low cost for later use where desired orto prevent the creation of a nuisance.

Where volatile reactants are used in conjunction with the formaldehydeno mechanical mixing of the ingredients is required. This results in aconsiderable saving in time, labor and other factors. Thus, in theseinstances, it is only necessary to charge the reactor with thelignocellulose and introduce the volatile materials into the reactorunder superatmospheric pressure. In addition, if desired, the reactantscan be changed or modified during the course of a run. This is notpossible to such a degree in a wet process where the charge generallycontains less than 50% of lignocellulose, and addition of reactantswould in many cases cause prohibitive amounts to go into solution.

A further advantage of utilizing a vapor process is that the volatilecontent of the reaction product which is primarily moisture can becontrolled. By using superheated steam with a suflicient degree ofsuperheat, products on the order of 1% or lower volatile content can beobtained. Under normal condition, to degrees of superheat at 300 poundsper square inch steam pressure will produce a product of 3-5% volatilecontent. Thus, the expensive drying step connected with wet processescan be avoided.

Because of rapid penetration of reactants under high pressure, largersized particles can be charged to the autoclave than would ordinarily beused, and a savings in size reduction cost made as a result of lowerpower requirements to reduce the treated material in comparison with rawlignocellulose.

In addition, where flat stock or preformed material is being made as ina sealed press, the products can be made much thicker and more uniformthan in an ordinary press which depends upon high platen temperaturesfor heat transfer, and in many cases requires almost prohibitive cycletimes.

The products of the reactions of this invention may be finished shapedmaterials or moldable compositions that may be used to make moldedproducts. Where the product is molded after the reaction, this productis preferably removed from the reaction vessel and then ground to -afine powder that is preferably not over 50 mesh in size. The finelydivided moldable material is heated to a temperature just sufficient tocause the material to flow and fill the mold under the pressure used.This temperature is kept sufiiciently low, however, that losses areminor and breakdown due to decomposition is kept to a minimum. Thepreferred temperature is between 250400 F.

The molding pressure may be any pressure sufiicient to cause thematerial to fill completely the mold and will vary depending upon theshape of the mold, the nature of the moldable material and otherfactors. in the preferred process to produce high density materials thispressure is between LOGO-10,000 pounds per square inch. The molding timeis only sufficient to cause the moldable material to fill the mold andset, and again will vary depending upon the type of mold being used, thetemperature, the nature of the moldable material and similar factors. Ingeneral, the molding time will vary between 0.2-15 minutes.

The flow of the moldable material of this invention is improved and ashorter time is required if a plasticizer is added.

Plasticizers in general which have been found to be effective with themoldable materials include water; aromatic compounds containing ahydroxyl group such as aniline, phenol and cresol, alcohols such asbenzyl, diethyleneglycol, glycerol, and furfuryl; nitrogen cornpoundssuch as fonnamide, urea, pyridine, and triethanolamine; and furfural.

The preferred plasticizers are water, furfural, aniline and phenol andthe quantity utilized may vary depending on the flow desired. Thepreferred quantity is between about 220%.

In particular, the choice of plasticizer will depend upon the end use ormethod of fabrication of the material. The reaction products themselvesare of a slow thermosetting nature. Thus, if a plasticizer such as waterwhich is incapable of thermoset is used, the material is essentially ofa thermoplastic nature. This is also true of the preferred plasticizersas a group; however, when desired, thermoset compositions can be made byusing furfural, aniline or phenol in conjunction with a catalyst and, ifdesired, other materials capable of copolymerization.

Materials which will function as catalysts include the oxides,hydroxides and carbonates of the alkali and alkaline earth metals. Thepreferred catalysts are the oxides of magnesium and zinc.

Among the materials which may be used with the thermosettingplasticizers as copolymers are hexamethylene tetramine, dimethylolurea,paraformaldehyde and urea.

Depending upon the set time required, about .05-5.0% of the catalyst andabout 05-10% of the copolymer are used.

If desired, thermoset products can be obtained without the use ofcatalysts or copolymers merely by heat treating the fabricated productsafter they have been molded or extruded.

If desired, products of density ranging from 0.2-1.3 specific gravitymay be produced in the high pressure reacting vessel itself withoutrequiring a subsequent molding operation as described above with highpressure molding. Here the finely divided lignocellulose and thereactant are mixed and the mixture cold pressed into the desired shapeor compacted in a sealed press. The compressed mixture is then heated inthe press or other high pressure vessel for the time required, at therequired temperature and pressure. The material when removed from thereaction vessel will then be found to be quite hard and strong. In theseinstances, the reactant may be any of those set out above.

The preferred amount of formaldehyde varies between about 05-15% byweight of the lignocellulose. The preferred amounts of various additivesthat may be used with formaldehyde are shown in the following table:

Additive: Preferred amount Sulfuric acid percent 0.1-5 Oxalic acid d00.1-8 Ammonium hydroxide do 1.0-15 Vinsol do 2.0-30 Cresol d0 2.0-25Sulfur do 1.0-20 Phenol residue d0 2.0-30 Sodium hydroxide do 0.1-5Sulfur dioxide p.s.i. gauge 2-50 Aluminum chloride percent 0.1-10 Ferricchloride d0 0.5-10 Phosphoric acid d0 0.1-20 Calcium chloride d0 1.0-10

. P.s.i. is pounds per square inch.

Steam may or may not be supplied to the reaction vessel depending uponthe result desired. If steam is used, it is preferably supplied at100-1000 pounds per square inch pressure and at a temperature of 400550F. In the event that a sealed press is used, the normal moisture contentof the wood as well as the reaction by-products may be used to build upto a predetermined pressure which can be maintained constant by ventingthe excess vapors produced. This pressure is preferably between 100-600pounds per square inch. Such a procedure eliminates the blow-upsencountered in treating wood in an ordinary hot press at hightemperatures, as well as drastically reducing press time, andpolymerizes a percentage of the gaseous and low molecular weightby-products to resinous-like materials which function as binders forlignocellulose particles. If desired, a two step process may be used inwhich the first step includes the pressure.

treatment and the second step includes venting the vapors to atmosphericpressure followed by a 2-10 minute heat treatment period before removingthe material from the press or the autoclave.

Example 1 Finely divided lignocellulose containing only its normalmoisture content of approximately 6% by weight was mixed with 20% byweight of the lignocellulose of 37% formaldehyde in water solution.Based on the weight of the lignocellulose the formaldehyde added wasapproximately 7.4%. The mixture was ball-milled for approximately /2hour to uniformly distribute the formaldehyde throughout the mass. Theblend was then placed in a heated autoclave, and steam was admitteduntil the pressure was 300 pounds per square inch and temperature was425 F. The mixture was held under these conditions for 20 minutes andthe interior of the autoclave was then vented. The reacting mixture wasremoved from the autoclave, and all particles which had consolidatedwere thoroughly broken up.

In a similar manner, lignocellulose was reacted with formaldehyde aloneand in conjunction with a number of other additives. The following tablesets forth the compositions, and the autoclave conditions under whichthese reactions were run.

Autoclave Percent Example Formal- Percent Additive dehyde Time, Temp,Press,

Min. F. p.s.i.

7. 4 None 30 440 300 7. 4 34% Sulfuric Acid+l% 20 440 300 Oxallc Acid.

7. 4 5% Ammonium Hy- 20 440 300 droxide.

7. 4 15% Vinso1+5% Am- 30 440 300 monium Hydroxide.

3. 7 10% Oresol+5% Am- 30 440 300 monium Hydroxide.

3. 7 15% Vinsol 35 440 800 3. 7 12% Sulfur-+45% Vinsol- 30 440 300 I 3.Phenol Residue-[4% 30 440 300 Sodium Hydroxide.

5.0 5 .s.i. Sulfur Dioxide.-- 20 440 300 5. 0 1% Aluminum Chloride. 400200 5.0 1% Ferric Chloride 25 440 300 5. 0 1% Phosphoric Acid".-- 25 400200 5.0 5% Vinso1+3% Cal- 20 440 300 clum Chloride:

l Paratormaldehydeil All percentages given herein are by weight of thelignocellulose.

Where solid materials such as Vinsol, sulfur, or phenol residue arereacted with the lignocellulose in conjunction with formaldehyde, theyare preferably very finely divided, and are thoroughly blended with thelignocellulose in a mixing device prior to the addition of theformaldehyde. Phenol residue is the condensation product of phenol withacetone and alpha-methylstyrene.

When inorganic salts, acids, or alkalies are used, they are preferablyadded as an aqueous solution, in an amount up to 20% of the weight ofthe lignocellulose. The solution concentration, of course, depends uponthe desired quantity of additive for the particular reaction. Where suchmaterials do not react with the formaldehyde, they can be added to theformaldehyde solution without prior dilution or solution andsimultaneously blended with the lignocellulose.

Where gases such as sulfur dioxide or ammonia are utilized, thelignocellulose mixture is placed in the autoclave, the autoclave isevacuated to remove air, and it is then filled with the gas to thedesired pressure. The formaldehyde may be used as a gas, solid or inliquid form as in aqueous solutions. It may also be supplied by amaterial capable of releasing formaldehyde.

Having described my invention 'as related to the embodiments set outherein, it is my intention that the invention be not limited by any ofthe details of description unless otherwise specified, but rather beconstrued broadly within its spirit and scope as set out in theaccompanying claims.

I claim:

1. The method of making a lignocellulose product, consisting essentiallyof: intimately mixing particles of lignocellulose with about 05-15% offormaldehyde by weight of the lignocellulose; and heating the resultingcomposition under confined pressure for between about 4-60 minutes andat between about 300-550 F. to combine chemically said formaldehyde withthe lignocellulose.

2. The method of making a lignocellulose product, consisting essentiallyof: intimately mixing particles of lignocellulose with about 05-15% offormaldehyde by weight of the lignocellulose; and heating the resultingcomposition under confined pressure in an atmosphere of steam forbetween about 4-60 minutes and at between about 300-5 50 F. to combinechemically said formaldehyde with the lignocellulose.

3. A lignocellulose product prepared by the method of claim 1.

References Cited in the file of this patent UNITED STATES PATENTS2,440,789 V-ander Pyl May 4, 1948 2,706,160 Clab Apr. 12, 1955 FOREIGNPATENTS 497,477 Great Britain Dec. 16, 1938

1. THE METHOD OF MAKING A LIGNOCELLULOSE PRODUCT, CONSISTING ESSENTIALLYOF: INTIMATELY MIXING PARTICLES OF LIGNOCELLULOSE WITH ABOUT 0.5-15% OFFORMALDEHYDE BY WEIGHT OF THE LIGNOCELLULOSE, AND HEATING THE RESULTINGCOMPOSITION UNDER CONFINED PRESSURE FOR BETWEEN ABOUT 4-60 MINUTES ANDAT BETWEEN ABOUT 300-550*F. TO COMBINE CHEMICALLY SAID FORMALDEHYDE WITHTHE LIGNOCELLULOSE.